Self-energized alternating current multiplier



Sept. 1939 P. T. FARNSWORTH 2,174,487

SELF-ENERGIZED ALTERNATING CURRENT MULTIPLIER Filed March 22, 1937 INVEN TOR. far/4 o T 4 940 WOR TH.

I F I M 1- i ATTORNEYS.C%

Patented Sept. 26, 1939 PATENT orFicE SELF-ENERGIZED ALTERNATING CURRENT a MULTIP LIER Philo T. Farnsworth, Springfield Township, Montgomery County, Pa., asslgnor, by mesne assignments, to Farnsworth Television & Radio Corporation, Dover,-Del., a corporation of Delaware Application March 22, 1937, Serial No. 132,324

5 Claims. (01. 250 -27 My invention relates to electron multipliers,

and more particularly toan electron discharge device wherein linear electron multiplication. takes place to the end thatan amplified output. may be secured of an electron input, the device being energized y self-generated alternating cur-, v

' tion, -I have pointed out that these multiplier rent. 1

Among the objects of my invention are: to pro.- vide a means and method for amplifying small electron currents; to provide a combined photoelectric cell and electron multiplier; to provide asystem wherein, in a single envelope linear electron multiplication takes placetogether with alternating current generation; to provide linear I generate self oscillations wheuproperly connected, and I have shown that in the latter instancev amplification of photo-emission; to provide a combined photo cell, electron multiplier, and driver within a single envelope, and utilizing at least certain electrodes in common; to providea three-electrode photo cell wherein electron multiplication of .the photo-emission is obtained with linear amplification; to provide a means and method of controllingthe output of a photo cell;

to provideameans and method of amplifying the and features of advantage, some of which, together with the foregoing, will be set forth in the fol-,

lowing description of specific apparatusembodying and utilizing my novelmethod. It is therefore tobe understood that my method is applicable to other apparatus'and that I do not limit f myself, in any way, to the apparatusof the pres ent application, as I may adopt various other apparatus'embodimentsutilizing the method, with:

in the scope of the appended claims. I

Referring to'the drawingz Figure ljis a diagrammatim sectional view of, one form 'of tube structure embodyingjmy invenj "tion; together with a circuit; diagram showing op erating con'nections. my invention:- Y Y I Inmy prior applications, for an Electron multiplying device, SerialNo. 692,585, filed October 23, 1937, Ihave described electron'multipliersand oscillators operating by .the repeated impact; of a 1 cloud -of electrons against a surface capable, of v I emittingsecondaries ata-ratio greater than unity, H and 1; have. disclosed and claimed .as one modifies tion of the device, a diode structure. I have also pointed out in both'of .these cited applications 1 that certain methods of treating surfaces for the production of secondaries at a ratio greater than unity leave the surfacein a condition wherein photo-emission may also be obtained. In addithe tubes usually operate at an equilibrium point where space charge tends to destroy linearity of output, when a controlled inputis utilized.

While it is possible, therefore, to build a multiplier wherein only two electrodes are utilized, and

where the initial electrons are supplied to it, it is not practical to allow the device to self-oscillate and thus obtain an output which is a direct function of the input. Such a structure, however,

would give a linear output providedthe electrodes,

are driven from another source.

I have discovered that by the addition of only a single additional electrodel am able to cause one part of thedevice to generate oscillations to. energize another portionof the device to the end that the driven portion will give a linear response to initial input electrons.

I In this present application ll have described my structure basically com-prising three elec-;

trodes with their appropriate circuits as being U suppliedwith initial electrons liberated by the ac- I tion of light, i. e., photo emission; but I wish it to ""be distinctly understood that the same action can be obtained with the same electrode structure and circuit, irrespectiveof whether the initial electrons are liberated time actionof light orare s M v liberated within operating space of theelectrodes Figure 2 is asimilar viewof a modification of s device is .capablenot'only'of amplifying photo-. emissionybut also any emission whose component electrons are liberated or otherwise project '7, 1933, Patent N0."2,071,515, dated Feb. 23, 1937; andanoscillation generaton' serialzNo. 733,837, I filed July 5,1934, Patent No. 2,071,516,; dated Feb.

fromothersources. In other words, my present ed into the operating'spaceof the device. Such modifications of my device arewell within the knowledge of those skilledin the art, andQWhile; ,I have shown the preferredconstruction which;

answers the. requirementsjeryeffectively, I do, .not-desire to be confinedto,thejprecise'details,- f,,.either of construction arrangement or" mode of application, but aim inmy claimstoicover allv forth in the appended claims. 4 pects of my invention maybe T V s more fully understood by direct reference to the which do not'involve a departure from the spirit and scope of the invention as set figures, vwhich'show two modifications, both at- I taining the same ruult.

helf of the inner surface of the cathode.

, In Figure 1, an envelope l is provided with a cylindrical cathode I perforated close to one end thereof with an aperture covered by a screen I. concentrically-positioned within the cathode 2 are twoadiacent cylindrical anodes, a photo cell anode l and an oscillator anode 8. These anodes are approximately the same size and sha e. and each one co-operates with approximately one- This inner-surface is sensitmed in this embodiment to perform a dual function; it must produce secondary electrons at a ratiogreater than unity upon electron impact therewith, and it must also in this particular adaptation product photoelectrons under the influence of light. Fortunately, a caesium-silver oxide surface will fulfill both of these anode G is connected to the positive end of an oscillator source I through a resonant circuit 9.

The cathode is grounded and the photo cell anode 5 is connected to the positive end of anode source I through a radio frequency choke l and a work circuit ll, diagrammatically represented in this case by a current indicator. A variable condenser I 2 is bridged across the two anodes.

In operation, as soon as the anode source I is connected to the oscillator anode i the electron multiplier comprising anode 6 and cathode 2 starts to operate as a multiplier oscillator. Electrons within the space bounded by anode 6 are P accelerated away from and against cathode 2 at a frequency determined by resonant circuit 9, and at each impact with the cathode generate additional secondary electrons until the current generated builds up to an equilibrium value. There will be, therefore, a variation of potential acrossv resonant circuit 9, and this potential is transmitted to anode through the variable condenser l2; the amount of energizing potential reaching anode 5 depending, of course, upon the adjustment of the condenser l2.

In the meantime, if light, as represented by arrow I 4, is directed into the interior of the oathode cylinder, this light illuminates theinterior wall of the cathode adjacent photo cell anode 5.

Photoelectrons are emitted'which are, because of the driving potential on anode 5, accelerated away from and against the inner surface of cathode 2 adjacent anode i, and are multiplied, the

multiplied electrons eventually being collected by .anode 5 as uni-directional pulses. Radio frequency choke l0 kee radio frequenc energy from passing through he work circuit, butthe uni-directional pulses received by anode =5 pass readily through this choke and through the work I circuit.

Thus, for an extremely small light value, high output currents are obtained, and as [9,174,491 a v v, a

; the photo cell multiplier combinationis driven the output will'be linear, or substantially so, within a wide range. Thefrequency of self-oscillation generated by the idevice'is, of course, determined by the resonant'f'circuit 8 and maybe, for example, between five and forty megacycles, depending on the number of secondary emission impacts desired in the photo cell end of the device. J

cathode l6 and an oscillator cathode I'I, whereas a single anode I 9 extends co-axi lly with both cathodes and over substantially th entire extent thereof. In this case, the fsingle node is supplied with steady potential from anode source 1,

and the oscillator cathode I1 is connected to the anode l9 through resonant circuit\9 grounded and blocking condenser 20. In this instance, the

output is taken directly from the photo cell cathode I6 through radio frequency choke I0 and work circuit H to ground, and the multiplication control is performed by the variable condenser I2 connecting the two cathodes. device through the photo cell cathode I6 and screen I in exactly the same manner as was described for Figure 1, and the operation\ is iden-' tical. There is little difference between\ the two embodiments shown except that under'\ certain circumstances itis possible to sensitize the two Light enters the cathodes differently in the embodiment shown in Figure 2 so that maximum photo-emission is obtained in the photocell end, and maximum secondary emission obtained in the oscillator end. This is an advantage rather than a drawback inasmuch as the best photo-emitters are also good secondary emitters, although the converse is not always true.

As explained above, it will-be within the knowledge of those skilled in the art to substitute an electron gun, a hot filament,or electrons liberated by other means within the driven structure for the photo-emitting combinatiomgand the use, of the device as a multiplying photo cell is illustrative only, although, as a photo cell it has a wide range of uses.

I claim:

1. An electron multiplier comprising a single envelope containing -a pair of diode electron multiplier structures, external circuit means for operating one of said structures as an electron multiplier, external circuit means for operating the other of said structures as an electron multiplier oscillator, and means for connecting the. oscillator output to energize said multiplier. I

2. An electron multiplier comprising an en velope containing a u'nipotential cathode surrounding a perforated anode, a second unipotential cathode surrounding said perforated anode,

obviously circuit means forcausingoscillation generation a by electron impact at a ratio greater than unity upon electron impact with one of said cathodes under the influence of said anode, means for energizing the other cathode from the os illations generated for electron multiplication by secondary emission, and means for liberating lectrons within the operating space of said latter cathode and said anode.

3. An electron multiplier comprising an envelope containing a unipotential cathode surrounding a perforated anode, a second unipotential and photoelectric cathode surrounding said perforated anode, circuit means for causing oscillation generation by electron impact at a ratio greater than unity upon electron impact with one of said cathodes under the influence of said anode,e mean s for energizing the other cathode from the'oscillations generated for electron multiplication'by secondary emission, and means for illuminating the latter cathode to liberate photoelectrons.

4. An electron multiplier comprising an envelope containing a unipotential cathode surrounding a perforated anode, a second unipotential cathode surrounding said perforated anode, circuit means for causing oscillation generation by electron impact at a ratio greater than unity upon electron impact with one of said cathodes under the influence of said anode, means for energizing the other cathode and said anode from the oscillations generated for electron multiplication by secondary emission, and means for liberating electrons within the operating space of said latter cathode and said anode, both of said cathodes being at the same potential.

5. An electron multiplier comprising an envelope containing a unipotential cathode surrounding a perforated anode, a second' unipotential cathode surrounding said perforated anode, circuit means for causing oscillation generation by electron impact at a ratio greater than unity upon electron impact with one of said cathodes under the influence of said anode, means for energizing the other cathode from the oscillations generated for electron multiplication by second,- ary emission, and means for liberating electrons within the operating space of said latter cathode and said anode.

. PHILO T. FARNSWORTH. 

